Self-tuned vibratory feeder

ABSTRACT

A driver for a vibratory feeder employs a D.C. field structure with an annular air gap in which is disposed concentrically both a stationary coil and a moving coil. The latter coil is mechanically coupled to drive the flexure supported tray. Both coils are connected in series opposition and have substantially zero resultant inductance. The coils, in series, are connected to both the output and input of an amplifier having a single-ended output to provide a self-excited oscillatory loop. A servo amplifier responding to the flyback voltage generated by the moving coil controls the gain of the main amplifier so as to provide for automatic velocity control. An A.C. shunt is selectably applicable to the main amplifier to suppress oscillation while the amplifier is maintained conductive for dynamic braking when a stop command is executed. The oscillatory wave shape is controlled to avoid high frequency components which give rise to acoustic noise.

Reiner' SELF-TUNED VIBRATORY FEEDER 1111 3,748,553 July 24, 1973 PrimaryExaminer-D 1 Duggan A ttorney Robert B. Sundheim [75] Inventor: RobertLeopold Reiner, Bethany,

Conn.

[73] Assignee: Cleveland Machine Controls, Inc., ABSTRACT Cleveland OhmA driver for a vibratory feeder employs a DC. field [22] Filed: Oct. 8,1971 structure with an annular air gap in which is disposedconcentrically both a stationary coil and a movin coil. [21] Appl'18762l The latter coil is mechanically coupled to driv e the flexuresupported tray. Both coils are connected in se- [52] US. Cl 318/128,310/27, 198/220 ries opposition and have substantially zero resultantin- [51] Int. Cl. 11021; 33/02 ductance. The coils, in series, areconnected to both [58] Field of Search 198/220 DC; 318/127, the outputand input of an amplifier having a single- 318/128, 129, 132, 118;310/27, 25 ended output to provide a self-excited oscillatory loop. Aservo amplifier responding to the flyback voltage [56] References Citedgenerated by the moving coil controls the gain of the UNITED STATESPATENTS main amplifier so as to provide for automatic velocity 2 844 7777/1958 Ross 318/128 Shun is 9 applicable 4/1'970 Helmsm 310/13 mainamplifier to suppress osclllatlon while the ampli- 2,287,223 6/1942Baird 318/128 fier is maintained conductive for dynamic braking 2 297,04 9 1942 swallow 310 27 x when a stop command is executed. Theoscillatory 2,287,880 6/1942 l-littson 318/128 wave shape is controlledto avoid high frequency com- 2,935,671 5/1960 ROSS 318/128 ponents whichgive rise to acoustic noise 3,654,540 4/1972 Honig et al. 318/118 19Claims, 3 Drawing Figures '5 2b Z9 Z7 7 3/435 Rah/5e W- 5 mm?- 537; MW22122 "$3 .33 l aac/ry Jen/o -i 3, OFCU/I' flee-15.40 J IVES Sup/ 15w/34 M 401. O/eca/r PAIENIEuJumMm sum 1 or 2 A a Q @N SELF-TUNEDVIBRATORY FEEDER The present invention relates to a system for driving aresonant spring mass system and, more particularly, to a system fordriving a vibratory feeder.

Vibratory feeders are employed for controlled movementor feed of bulkmaterial from point-to-point. Such feeders are useful wherever smallparts or particulate material is to be transferred from a supply zone toa utilization point. A typical use for a feeder of this type is inconjunction with packaging machinery and the like.

One form of vibratory feeder commercially available prior to the presentinvention employs an electromagnetic driver having a stationarylaminated iron core excited by a field coil for vibrating throughmagnetic attraction a leaf spring mounted armature mass. The maincomponent of the spring mounted mass is the feed tray or trough overwhich the material is fed. The frequency at which the structure isvibrated depends upon the frequency of the alternating current poweringthe electromagnet. Generally, thisis 60 hertz.

The known type of feeder is significantly load sensitive in that asmaterial is added to the tray the resonant frequency of the spring massstructure changes. The

' nature of the drive is such that as the resonant frequency changes theamplitude of vibration also changes. The amplitude is a maximum onlywhen the mechanical resonant frequency of the moving structure is equalto the frequency of the power source. Since the mechanical resonantfrequency is affected by the load added to the tray or trough, thefeeder described above is normally tuned to have a no-load mechanicalresonant frequency somewhat above the frequency of the power source. Asload is added the mechanical resonant frequency will drop towards thesource frequency. Unfortunately, this mode of operation sacrificesefficiency and such devices are readily overloaded and caused to stall.In order to minimize the sensitivity to varying load, the feed troughsare made relative heavy with an attendant consumption of waste power.

With the foregoing in mind, it is an object of the present invention toprovide a system for driving a resonant spring mass system and therebyprovide a vibratory feeder which is inherently more flexible in itsoperation than feeders heretofore known.

A further object of the present invention is to provide a driver for aresonant spring mass system of novel construction.

A still further object of the present invention is to provide avibratory feeder capable of operation with substantially lighter pans orfeed trays than feeders heretofore known.-

Another object of the present invention is to provide a system fordriving a resonant spring mass system which is substantially independentof line voltage and substantially stall-proof.

In accordance with the present invention, there is provided a system fordriving a resonant spring mass system which comprises a driver having adriving coil mounted for reciprocation in an air gap of a magnetic fieldstructure. Means are provided for coupling the driving coil to thespring mass system. An amplifier having an input and an output isprovided with its input and output both coupled to the driving coil.Thereby, a self-excited oscillatory loop circuit is developed fordriving the driver at the mechanical resonant frequency of the combineddriver spring mass combination.

The invention will be better understood after reading the followingdetailed description of a presently preferred embodiment thereof withreference to the appended drawings in which:

FIG. 1 is a diagrammatic longitudinal sectional view through the driverand coupled vibratory feed tray assembly constructed in accordance withthe present invention;

FIG. 2 is a block diagram for the purpose of explaining the basic systemcircuit for driving the resonant mechanical system; and

FIG. 3 is a detailed electrical schematic diagram of the control circuitfor driving the driver element.

Throughout the several figures of the drawings the same referencenumerals are used to designate the same or similar parts.

Referring now toFIG. 1, there is designated generally by the referencenumeral 10 a typical trough or tray which may have any suitablecross-section, e.g., rectangular, circular or the like. The tray 10 issecured by any suitable means to a bracket or support 11 which ismounted by flexures l2 and 13 on a base member 14. The base member 14 isjoined to the field structure of an electro-mechanical driver 15 whichhas its bottom plate 16 secured to another base member 17. A cylindricalpermanent magnet section 18 provides a magnetic field across an annularair gap 19 formed between an outer pole piece and a radially inner corepiece 20. A driving coil 21 is mounted in any suitable manner forreciprocation in the air gap 19. The coil 21 is shown suspended at thelower end of the cylindrical skirt portion 22 of a table or armaturemember 23 which is coupled by the bolt 24 to the bracket 11 forimparting vibratory motion thereto. A stationary compensating coil 25 isdisposed in the air gap 19 concentrically related to the driving coil2!. As seen in FIG. 1, the coil 25 is wound directly upon the inner corepiece 20. For reasons which will be evident hereinafter, thecompensating coil 25 has substantially the same number of turns ofsubstantially the same size conductor at substantially the same pitch asthe driving coil 21, such that the inductance of the compensating coilis approximately the same as the inductance of the driving coil.

It is to be understood that the field structure illustrated in thedrawings is only exemplary and may be modified in ways well known tothose presently skilled in the art. While a permanent magnet type fieldis shown and preferred, a field which is excited by a D.C. power sourcemay also be employed. Furthermore, the polarization of the field magnetmay be reversed from that shown in FIG. 1.

Flexures l2 and 13 may take any well known form and are here shown ascomposite plate elements having the desired flexural characteristics.The pan or trough 10 may be secured to the bracket 11 by screws or otherreadily removable means such that the pan 10 may be readily replaced byanother of different size or configuration.

Referring now to FIG. 2, there is shown in generalized form theelectrical system for powering the electro-mechanical driver 15 whichdrives the resonant mechanical system 26. The system 26 encompasses thetrough 10, the support bracket 11, flexures l2 and 13, and the entiremoving element of the driver 15, along with any load or contents in thetrough 10.

Electric power is supplied to the electro-mechanical driver from a poweramplifier 27 which receives its input signal from a high gain voltageamplifier 28 after such signal passes through a phase lag wave shapingcircuit 29. A regenerative feedback path is provided from theelectro-mechanical driver through a phase lead wave shaping circuit 30to a summation point 31 which feeds the input of the voltage amplifier28. Collectively, the components within the broken line box 27a may beconsidered an amplifier whose output and input are both connected to thedriver 15.

A start command circuit 32 also supplies signal to the summation point31. A further feedback path is provided from the electro-mechanicaldriver 15 through a velocity servo circuit 33 to the power amplifier 27.Finally, a start-stop control circuit 34 supplies control to both aninput of the power amplifier 27 and the velocity servo circuit 33.

The closed loop circuit that can be traced from the output of voltageamplifier 28 through wave shaping circuit 29, power amplifier 27,electro-mechanical driver 15, wave shaping circuit 30, and summationpoint 31 to the input of amplifier 28 provides for selfexcitedoscillation. The frequency of oscillation is determined by themechanical resonant frequency of the combined resonant mechanical system26 and moving component of driver 15. The velocity servo circuit 33provides a gain control function regulating the gain of the poweramplifier 27 as a function of the velocity of the driver 15 in order totend to maintain such velocity at a constant level. For a furtherunderstanding of the operation of this system,reference should be had tothe detailed schematic diagram shown in FIG. 3, to which attention isnow directed.

Referring to FIG. 3, to the extent that components can be specificallygrouped and identified relative to the block diagram of FIG. 2, suchcomponents are designated by the same reference numerals. Thus, the waveshaping circuit 29 is shown within the broken line box 29, while thewave shaping circuit 30 is shown in a similar broken line box 30.

A power transformer 35 has its primary winding 36 connected through amain on-ofi switch 37 and a fuse or other overload protective device 38to input terminals 39 for connection to the conventional power mains. Inthe present embodiment, the power mains may be the usual l-volt 60 hertzsupply. Transformer 35 has a secondary winding 40 with a center tap 41connected to a point of reference potential here indicated as ground.One end of winding 40 is connected through a unidirectional device ordiode 42 to a'negative voltage bus or lead 43. The other end of winding40 is connected through a similar unidirectional device 44 to the samelead 43. A smoothing capacitor 45 is connected between the bus 43 andground. A positive voltage bus 46 is connected through a thirdunidirectional device 47 to one end of winding 40, as shown. A smoothingcapacitor 48 is connected between the bus 46 and ground.

A voltage divider composed of resistor 49 in series with a zener diode50 is connected between the negative bus 43 and ground. The junctionpoint 51 between the resistor 49 and the zener diode 50 is connectedthrough a fixed resistor 52 to the positive input of an operationalamplifier which performs the function of the voltage amplifier 28. Thenegative input of the operational amplifier 28 is connected to thejunction 51 by an adjustable resistor 53 in series with a fixed resistor54. A feedback resistor 55 is connected between the output 56 of theoperational amplifier 28 and its negative input. Voltage for operatingthe operational amplifier 28 is supplied thereto from the negative busover the lead 57 and from ground over the lead 58.

The output 56 of the amplifier 28 is connected to ground through aresistor 59 in series with a resistor 60 which, in turn, is shunted by acapacitor 61. The components 59, 60 and 61 constitute a low pass type offilter constituting the wave shaping circuit 29 for a purpose to bedescribed.

An output of the filter or wave shaping circuit 29 is obtained over thelead 62 which is connected to an input of the power amplifier 27. Morespecifically, the lead 62 is connected to the base electrode 63 of alP-N-P transistor 64 whose collector electrode 65 is connected throughresistors 66 and 67 in series to the negative bus 43. A capacitor 68shunts the resistor 67 while a capacitor 69 is connected between thecollector electrode 65 and ground. The emitter electrode 70 oftransistor 64 is connected to ground through a parallel network. Onecomponent of the parallel network is the resistor 71. Another componentof the parallel network is the resistor 72 in series with the P-N-Ptransistor 73. As shown, the resistor 72 is connected from the emitterof transistor 64 to the collector electrode 74 of transistor 73 whoseemitter electrode 75 is connected to ground. The junction 76 between theemitter 70 and the resistors 71 and 72 is also connected through aresistor 77 to the negative bus 43. Transistor 73 also has a baseelectrode 78 which is connected to ground through a resistor 79.

The output from transistor 64 is obtained at the junction 80 between theresistors 66 and 67. The junction 80 is connected to the base electrode81 of an N-P-N transistor 82 which has its emitter electrode 83connected to the negative bus 43 through a resistor 84 and which is alsoconnected to the base electrode 85 of a further N-P-N transistor 86. Thecollector electrode 87 of transistor 82 is connected to the collectorelectrode 88 of transistor 86 at a junction 89. The transistor 86 has anemitter electrode 90 which is connected through a resistor 91 to thenegative bus 43. It will be recognized that the transistors 82 and 86are connected in a conventional Darlington arrangement.

The junction 89 represents the output point of the single-ended outputof power amplifier 27 and is connected to a terminal 92. As shown,terminal 92 is connected through the windings 21 and 25 in seriesopposition to ground via a second terminal 93. The windings 21 and 25correspond to the driving coil and stationary coil, respectively, shownin FIG. 1. Since the windings are connected in series opposition andhave approximately equal inductance they provide an effective resistiveload as seen from the terminals 92 and 93.

Junction 89 is also connected through a resistor 94 back to the junction76 at the emitter 70 of transistor 64. A further connection is providedfrom junction 89 through lead 95 to an input of the wave shaping circuit30 and through a capacitor 96 to a junction 97. The junction 97 isconnected to ground through an adjustable resistor 98 and is connectedthrough a capacitor 99 in series with a resistor 100 to the positiveinput of amplifier 28. It will be recognized that the components 96 and98 constitute a high-pass type filter network. It will also beunderstood that the wave shaping circuit 29 tends to cause a lag involtage with respect to the voltage passing therethrough, while thecircuit 30 tends to cause a lead in the voltage passing through it. Thephase lead introduced by circuit should be substantially equal andopposite to the lag introduced by circuit 29 for any given frequency.Resistor 98 can be adjusted to achieve this relationship.

Junction 89 at the output of the power amplifier is also connectedthrough the unidirectional conducting device or diode 101 to a point 102which is connected to ground through a series arrangement of a resistor103 and a capacitor 104. The point 102 is also connected through aparallel arrangement of a capacitor 105 and an adjustable resistor 106to a resistor 107 which has its opposite end connected at a point 108 tothe base electrode 109 of a P-N-P transistor 110. The transistor 110 hasits emitter electrode 111 connected to the junction between baseelectrode 78 of transistor 73 and resistor 79. A collector electrode 112of the transistor 110 is connected through a resistor 113 to a bus 114which leads to the junction 51. The bus 114 is connected also through aresistor 115 to a fixed contact 116 of a switch 1 17. Switch 117 has itsmoving element or armature 118 connected through a resistor 119 to thepoint 108. Switch 117 is of the double-throw type having a second fixedcontact 120 which is connected to a terminal 121. A second terminal 122is provided connected to the bus 114. As shown by the phantom lines, aremote external resistor may be connected be tween the terminals 121 and122.

Point 108 is connected also through a resistor 123 and a capacitor 124to ground. The junction 125 between resistor 123 and capacitor 124 isconnected over a lead 126 to a fixed contact 127 associated with a relaydesignated generally by the numeral 128. A second fixed contact of relay128 is shown at 129 and is connected to the negative bus 43. A relayarmature 130 associated with contacts 127 and 129 is connected throughresistors 131 and 132 in series to the positive bus'46. The junction 133between resistors 131 and 132 is connected through a capacitor 134 toground. The junction 133 is connected also through a unidirectionalconducting device or diode element 135 to the junction 136 betweenresistors 137 and 138 which are connected between the negative bus 43and ground.

Another connection extends from the lead 62 over lead 139 to a junctionpoint 140. The junction 140 is connected through a resistor 141 inseries with a capacitor 142 to a junction 143. Junction 143 is connectedto a fixed contact 144 of relay 128 and is also connected to groundthrough resistors 145 and 146 in series. A unidirectional conductingdevice 147 is con nected in shunt with the resistor 146. An armature 148of relay 128 associated with the contact 144 is connected, as shown, toground.

Relay 128 has a winding 149 which is connected at one end throughresistor 150 to the negative bus 43 and at its other end to a fixedcontact 151 of a switch 152. A unidirectional conducting device 153 isconnected in parallel with the winding 149. The armature 154 of switch152 is connected to ground.

A voltage divider consisting of resistor 155 connected in series withpotentiometer 156 and resistor 157 is connected between the positive bus46 and ground. A zener diode 158 is connected from ground to thejunction 159 between resistor 155 and potentiometer 156. The slider 160on potentiometer 156 is connected through a resistor 161 to the junction140.

Finally, it will be seen that the start command circuit 32 comprises acapacitor 162 connected in series with a resistor 163 between ground andthe negative input of amplifier 28.

The operation of the circuit of FIG. 3 will now be explained. For thesake of discussion, assume that the switch 152 controlling thestart-stop function is in the position shown in FIG. 3. When power isturned on to the equipment by closing switch 37, voltage rapidly buildsup between the negative and positive buses 43 and 46. Since the switch152 maintains the circuit through the winding 149 of relay 128 open, therelay contacts 148 and 130 will be in the position shown in thedrawings. It should be assumed that all of the capcitors in the circuitare initially discharged. As voltage appears on bus 43, the operationalamplifier 28 will become energized. At the same time current will flowthrough a circuit which can be traced from ground through capacitor 163,resistor 163, resistor 54, resistor 53, junction 51, and resistor 49 tothe negative bus 43. This current will flow initially until a blockingcharge develops across capacitor 162. Current will likewise flow througha similar circuit traced from ground through resistor 98, capacitor 99,resistor 100, resistor 52, junction 51, and resistor 49 to bus 43.However, resistor 52 is chosen somewhat larger than the maximum totalresistance of resistors 53 and 54 in series. This coupled with the factthat resistor 98 provides additional resistance in series with capacitor99 ensures that the voltage on the negative input of the amplifier 28will tend to approach closer to ground potential than the potential atthe positive input to the amplifier whereby the amplifier will be urgedto assume the con dition where its output approaches the potential ofthe negative bus. A potential at point 56 which approaches the negativebus value will tend to render transistor 64 conducting which, in turn,renders transistors 82 and 86 conducting so as to cause current to flowthrough the windings 21 and- 25 from ground. In the absence of the startcommand network 32 it would be possible for the operational amplifier 28to assume initially when power is first applied a condition whereby itsoutput approaches ground potential. If this were to occur, it wouldcause the transistors 64, 82 and 86 to be rendered non-conductingthereby precluding the flow of current through windings 21 and 25. Insuch case, the circuit would not start. Thus, the capacitor 162 inseries with resistor 163 ensures that amplifier 28 assumes a conditionat tum-on which causes the transistors in the power amplifier to becomeconductive.

Upon the commencement of current flow through windings 21 and 25, themoving element of the driver 15 will be displaced against the resistanceof the spring flexures. As movement slows upon the moving elementapproaching the end of its limit of travel, the back e.m.f. developed bywinding 21 will decrease causing the voltage at point 89 to move towardthe potential at ground. This voltage signal is fed back through lead 95and wave shaping circuit 30 to the positive input of amplifier 28causing a reversal in condition of the amplifier 28; that is, the groundpotential going signal applied to the positive input will cause theoutput to shift from that nearest the negative potential towards thepotential at ground. This shift in output from amplifier 28 passesthrough the shaping circuit 29, being delayed somewhat in phase, andcauses transistor 64 to become less conductive. This is amplifiedthrough transistors 82 and 86 appearing first as a reduction in thesupply of current to windings 21 and 25 followed by complete cut-off.

The stored energy in the fiexures associated with the resonantmechanical system causes the moving element including driving coil 21 toreturn towards its original position. A voltage is developed at terminal92 which is applied to point 89 of the circuit of opposite polarity tothat initially applied to the winding. This voltage is of a polarity tocause current to flow through rectifier 101 and through the smallphasing resistor 103 into the capacitor 104 which serves as a chargestorage element. It should be understood that normally capacitor 104would have a charge thereon such that its plate furthest removed fromground is negative relative to ground potential. The effect of passingcurrent through diode 101 is to reduce this negative potential or chargeon capacitor 104. The extent to which such charge is reduced isproportional to the fly-back velocity of the moving coil 21. Since themechanical system is free to oscillate, the coil 21 will reversemovement again causing the potential at point 89 to reverse for a secondtime tending to move in the negative direction. This will, in turn,reverse the condition of amplifier 28 driving its output in the negativedirection causing transistors 64, 82 and 86 to turn on again, repeatingthe cycle. It should now be apparent that the loop circuit willoscillate at a frequency determined by the mechanical resonant frequencyof the resonant mechanical system.

The gain of the power amplifier represented by transistors 64, 82 and 86is determined by the impedance between junction 76 and ground. Thisimpedance is a function of the conductivity of transistor 73. Theconductivity of transistor 73 is, in turn, controlled by theconductivity of transistor 110. Together, transistors 73 and 110constitute an auxiliary amplifier. When power is first turned on currentflows through capacitor 124 and resistors 123, 119, and 115 applying avoltage to base electrode 109 of transistor 110 which tends to reducethe conductivity of that transistor. This action tends to reduce theconductivity of transistor 73 which reduces the conductivity oftransistor 64 and, therefore, the overall gain of the power amplifier.By initially restricting the gain of the amplifier the system avoids theoccurrence of high velocity transients.

After an initial start-up interval, the capacitor 124 will reach maximumcharge causing transistor 110 to conduct more heavily and thereby toincrease the gain of the power amplifier 27. As oscillation of thedriver element builds up, the voltage across capacitor 104 will changein a direction tending to render transistor 110 less conductive andthereby lowering thegain of the power amplifier. It will be seen thatthis action tends to oppose change in the velocity of the movingelement.

It should now be readily apparent that adjusting the resistor 106 canalter the level at which the velocity servo circuit 33 maintains thegain of the power amplifier and, thereby, the velocity of the driverelement 15. If the switch 117 is manipulated such that its movingelement 118 engages fixed contact 120 any external resistor connectedbetween terminals 121 and 122 will be substituted for the fixed resistor115. Adjustment of such external resistance will also have the effect ofvarying the level established by the velocity servo circuit 33.

Adjustable resistor 53 is used to trim the loop phase angle and produceoptimum output efficiency and good wave form. The zener diode 50establishes a stabilized voltage at point 51 for setting the referencepoint for operation of amplifier 28 as well as for supplying voltage tothe transistor in the velocity servo circuit.

The operating point of transistor 64 is adjusted through potentiometer156. Preferably, this operating point should be established somewhatmidway between the potential of the negative bus 43 and ground.

When it is desired to stop operation of the vibratory feeder, the switch152 is manipulated to the stop position engaging contact 151. Thisenergizes relay winding 149 causing movable contacts 130 and 148 toshift engaging, respectively, fixed contacts 127 and 144. When contact148 engages fixed contact 144, the junction 143 is connected to groundplacing the low impedance A.C. network consisting of capacitor 142 andresistor 141 between the lead 62 and ground. This provides an effectiveA.C. short for the A.C. signal appearing at the output of amplifier 28and shunts the input of the power amplifier 27. At the same time, whencontact 130 engages fixed contact 127, a charge previously stored oncapacitor 134 is transferred to capacitor 124. The polarity of thecharge is such as to initially maintain transistor 110 in a conductivecondition. This maintains transistors 73, 64, 82 and 86 conductive toprovide a low impedance shunt path for current flowing through coils 21and 25, thereby effecting dynamic braking of the moving element. Currentsupplied from the positive bus 46 through resistors 132 and 13] ensuresthat both capacitors 134 and 124 will discharge after a short interval.The interval is long enough, however, to ensure effective dynamicbraking of the moving element.

When it is desired to start the vibratory feeder again, the switch 152is manipulated to the start position interrupting the energization ofrelay winding 149 causing its contacts 130 and 148 to return to thecondition shown in the drawings. When contact 148 leaves contact 144 theA.C. short is removed from across the output of amplifier 28. Whencontact 130 of relay 128 engages fixed contact 129 a circuit iscompleted for recharging capacitor 134 in a negative direction.,At thesame time, the connection to the junction is interrupted such thatcapacitor 124 is free to charge with point 125 moving in the negativedirection. This causes transistor 110 to turn on gradually such that thegain, and thereby, the excitation of winding 21 increases graduallycausing smooth commencement of vibration.

The rectifier 147 is included in order that a voltage may be developedacross capacitor 142 through rectification of the signal appearing onlead 62 which voltage functions to render transistor 64 more conductivewhen the stop command is initiated.

It should be understood that if capacitor 134 and its associatedinterconnections were not provided for transferring a charge tocapacitor 124 when the stop command is initiated, the transistor 110would immediately become non-conductive precluding dynamic braking ofthe moving element.

The capacitors 68 and 69 are provided for suppressing parasiticoscillation in the power amplifier section. In addition, the capacitor69 is preferably selected large enough to perform a filtering orsmoothing action with respect to the signal being amplified.

In the absence of wave shaping circuits 29 and 30 the circuit wouldoscillate with abrupt square wave characteristics. It has beendiscovered that this mode of oscillation is accompanied by excessiveacoustic noise emanating from the moving element. It was also discoveredthat the noise could be reduced appreciably by smoothing the wave shapethrough the inclusion of the lowpass type filter in the output ofamplifier 28. However, this filter introduces a phase'lag on the voltageand must be compensated for by the inclusion of a phase lead circuit inthe feedback path which circuit appears as shaping circuit 30.

Rectifier 135 functions to block reverse voltage from being applied tocapacitors 134 and 124. A positive charge on capacitor 124 wouldfunction to delay startup of the circuit when vibration is desired.

It should be observed that a common coil is employed both to perform thedriving function relative to the driver 15 and the feedback function forclosing the oscillatory loop circuit. The purpose of the stationary coil25 is to eliminate the transient effect due to a hysteresis phenomenon.Without the stationary coil it was found that an undesirable lowfrequency phase shift was introduced adversely affecting operation ofthe system. By introducing the stationary coil having substantially thesame inductance as the moving coil and connected in series opposition asshown in the drawings, the undesirable operation was fully eliminated.Inclusion of the stationary coil resulted in increased amplitude dynamicrange and increased ability to maintain constant velocity through thecontrol of the servo circuit.

While FIG. 3 shows the stationary coil located nearest ground, it shouldbe understood that the moving coil may be interchanged therewith.Furthermore, while the stationary coil has been shown in FIG. 1 aslocated nearest the inner core, it is possible to interchange the twocoils with the stationary coil being located on the outer pole face.

Where a lesser dynamic range of control is required, the transistor 110with its resistors 79 and 113 may be eliminated and replaced by a directconnection between junction 108 and base electrode 78 of transistor 73.

In those cases where it is not important that the device be capable ofrapid start and stop function, the start-stop control circuit 34 may beomitted with a simple connection being established from junction 125 toground through a start-stop switch. Such switch in the start commandposition should be open circuited while in the stop command condition itshould place a short across capacitor 124 to ground.

Typical values of the circuit constants which have been foundsatisfactory for the circuit of FIG. 3 are set forth in the followingtabulation. Unless otherwise indicated, all values of resistances are inohms and have 55 watt ratings and all values of capacitances are inmicrofarads. Resistance values followed by an asterisk indicate apotentiometer. K X 10 RESISTORS Ref. Ref.

No. Value No. Value No. Value 49 1.5K 84 lK 132 22K 52 5.6K 91 0.25/lW.137 [5K 53 5K 94 3.3K 138 470 54 470 98 2.2K-68K 141 I0 55 47K [00 47K145 lOK 59 K 103 4.7 146 K 60 4.7 K 106 5K 150 33 10 66 470 107 680 I551.5K 67 2.2K 113 1 IK 156 5K 71 [K 115 4.7K 157 470 72 47 119 2.2K 161lOK 77 lOK 123 220 163 47K 79 4.7K 131 330 CAPACITORS DIODES ANDTRANSISTORS Ref. Ref. No. Value No Type 45 14,000 42 AISA 48 I00 44 AISA61 l-35 V D C 47 1N5059 68 0.1 50 1N524l 69 0.47 64 2N4125 96 0.22 732N4l25 99 2-50 V.D.C. 82 2N3054 104 500-6 V.D.C. 86 2N3055 105 20-30V.D.C. 101 lNS059 124 300-l5 V.D.C. 2N4l25 134 40-50 V.D.C. 135 MAl703142 300-15 V.D.C. 147 MAI703 162 20 153 MAl703 158 lN524l Relay Coil 14924 volt. Transformer 35 t 25 volt output Operational Amplifier 28 pA74lCHaving described the presently preferred embodiment of the invention itwill be understood that various changes in construction can be madewithout departing from the true spirit of the invention as defined inthe appended claims.

What is claimed is:

1. A system for driving a resonant spring mass system comprising adriver having a driving coil mounted for reciprocation in an air gap ofa magnetic field structure, and means for coupling said driving coil tosaid spring mass system; an amplifier having an input and an output; andmeans coupling said driving coil to both said input and said output ofsaid amplifier to form a self-excited oscillatory loop circuit fordriving said driver at the mechanical resonant frequency of the combineddriver-spring mass combination, said output of the amplifier issingle-ended for supplying current in only one direction to said drivingcoil during alternate half cycles of the reciprocation thereof, andfurther means are coupled between said driving coil and said amplifierfor responding to the voltage produced across said driving coil duringthe opposite half cycles of the reciprocation thereof for regulating thegain of said amplifier in a directiontending to maintain said voltageconstant.

2. A system according to claim 1, wherein said loop circuit includesmeans for preventing abrupt voltage changes in the oscillatory voltagepresent in said output of the amplifier.

3. A system according to claim 2, wherein said means for preventingabrupt voltage changes comprises a first wave shaping circuit in saidamplifier and a second wave shaping circuit in the coupling between saiddriving coil and said input of the amplifier, one of said wave shapingcircuits producing a phase lag on voltages passing therethrough and theother of said wave shaping circuits producing a corresponding phase leadon voltages passing therethrough such that the net phase change causedby said first and second wave shaping circuits is substantially zero.

4. A system according to claim I, wherein said further means comprisesan auxiliary amplifier circuit, and means for adjusting the gain of saidauxiliary amplifier.

5. A system according to claim 4, wherein said further means comprises aunidirectional conducting device connected in series with a chargestorage element across said output of said amplifier, the poling of saidunidirectional conducting device being such as to be substantiallynon-conducting for current in said one direction.

6. A system according to claim 1, wherein control means are provided forstarting and stopping oscillation of said oscillatory loop circuit, saidcontrol means comprising means for abruptly suppressing the passage ofA.C. signals around said loop when it is desired to stop oscillation,and means operative upon initiation of a stop command for temporarilycausing operation of said further means in a direction tending tomaintain the gain of said amplifier at a maximum level whereby saiddriving coil is dynamically braked.

7. A system according to claim 5, wherein said driver further includes astationary compensating coil disposed in said air gap concentricallyrelated to said driving coil and connected in series opposition to saiddriving coil.

8. A system according to claim 7, wherein said compensating coil hassubstantially the same number of turns of substantially the same sizeconductor at substantially the same pitch as said driving coil such thatthe inductance of said compensating coil is approximately the same asthe inductance of said driving coil.

9. A system for driving a resonant spring mass system comprising adriver having a driving coil mounted for reciprocation in an air gap ofa magnetic field structure, and means for coupling said driving coil tosaid spring mass system; an amplifier having an input and an output; andmeans coupling said driving coil to both said input and said output ofsaid amplifier to form a self-excited oscillatory loop circuit fordriving said driver at the mechanical resonant frequency of the combineddriver-spring mass combination, control means for starting and stoppingoscillation of said oscillatory loop circuit, said control meanscomprising means for abruptly suppressing the passage of A.C. signalsaround said loop when it is desired to stop oscillation, and meansoperative upon initiation of a stop command for temporarily causingoperation of said amplifier at maximum gain whereby said driving coil isdynamically braked.

10. A system for driving a resonant spring mass system comprising adriver having a driving coil mounted for reciprocation in an air gap ofa magnetic field structure, and means for coupling said driving coil tosaid spring mass system; an amplifier having an input and an output; andmeans coupling said driving coil to both said input and said output ofsaid amplifier to form a self-excited oscillatory loop circuit fordriving said driver at the mechanical resonant frequency of the combineddriver-spring mass combination, control means for starting and stoppingoscillation of said oscillatory loop circuit, said control meanscomprising means for causing said amplifier to operate momentarily atminimum gain upon initiation of a start command to prevent a highvelocity transient in the initial motion of said driving coil.

11. A control device for energizing an electromechanical driver fordriving a resonant spring mass system, said device comprising incombination a high gain voltage amplifier having an input and an output,a power amplifier having an input and a single-ended output, a low passtype filter network interconnecting said output of said voltageamplifier with said input of said power amplifier, said output of saidpower amplifier having a first output terminal connected to a point offixed potential and having a second output terminal,

a high pass type filter network interconnecting said second outputterminal with said input of said voltage amplifier for providingregenerative feedback thereto, said filters being arranged to imposesubstantially equal and opposite phase shift on the signal voltagepassing therethrough, and means selectably operable for selectivelypreventing oscillation around the loop including said two amplifierswhen said output terminals are connected to an electro-mechanicaldriver.

12. A control device according to claim 11, wherein said means forpreventing oscillation comprises a circuit having a low impedance forA.C. signals, and means for selectably connecting said low impedancecircuit in shunt with said input of the power amplifier.

13. A control device according to claim 11, further comprising aunidirectional conducting device connected in series with a chargestorage element between said two output terminals, the poling of saidunidirectional conducting device being such as to be substantiallynon-conducting for current supplied by said power amplifier, and anauxiliary amplifier having an input coupled across said charge storageelement and having an output connected to said power amplifier forregulating the gain of the latter as a function of the charge on saidstorage device and in a direction tending to maintain said chargeconstant.

14. A control device according to claim 13, further comprising meansoperative along with said means for preventing oscillation, uponinitiation of a stop command, for temporarily causing operation of saidauxiliary amplifier such as to tend to maintain the gain of said poweramplifier at a maximum level whereby an effective low impedance shuntappears temporarily across said output terminals.

15. A vibratory feeder comprising in combination a feeder tray; springmeans mounting said tray for vibratory feed motion; a driver having adriving coil mounted for reciprocation in an air gap of a magnetic fieldstructure; means coupling said driving coil to said tray for impartingsaid motion thereto; an amplifier having an input and an output; andmeans coupling said driving coil to both said input and said output ofsaid amplifier to form a self-excited oscillatory loop circuit fordriving said driver at the mechanical resonant frequency of the driverand tray in combination with any load on the tray; said amplifierincluding means for, when activated, applying unidirectional current toflow in a given direction through said coil; and said coupling meansincluding control circuit means connected to said coil for activatingsaid current applying means in response to a voltage of a first polaritybeing developed across said coil.

16. A vibratory feeder according to claim 15, wherein said amplifiercomprises means for constraining the wave shape of voltage signalspassing through the amplifier to that which causes minimum audible noiseto be generated by movement of said driver-tray combination.

17. A vibratory feeder comprising:

a feeder tray;

spring means mounting said tray for reciprocal vibratory movement;

a driver including magnetic field producing means for developing amagnetic field across an air gap and a driving coil coupled to saidfeeder tray and to said spring means for reciprocal vibratory movementtherewith in first and second opposing directions in said air gapagainst respectively opposing forces exerted thereon by at least saidspring means so that as said coil moves through said magnetic field avoltage of a first polarity is induced in said coil as it travelsthrough said field in said first direction and a voltage of an oppositesecond polarity is induced in said coil as it travels through said fieldin said second direction;

activatable circuit means for, when activated, applying unidirectionalcurrent to said coil to flow therethrough in a given direction todevelop driving forces imparting movement to said coil in said firstdirection;

first control circuit means connected to said coil and respectivelyresponsive to a said induced voltage of 15 said first polarity foractivating said current applying circuit means and to a said inducedvoltage of said second polarity for tie-activating said current applyingmeans whereby unidirectional current is periodically applied in saidgiven direction to said coil at a frequency essentially correspondingwith the mechanical resonant frequency of the driver coil, spring meansand tray and any load carried by the tray.

18. A vibratory feeder as set forth in claim 17 wherein said currentapplying circuit means includes semiconductor means for, whenconducting, completing a path for said unidirectional current to flow insaid given direction through said coil with the amount of currentflowing therethrough varying as a function of the level of conductivityof said semiconductive means.

19. A vibratory feeder as set forth in claim 18 wherein said currentapplying means includes amplifier means for varying the magnitude ofcurrent flowing through said semi-conductor means and said coil, secondcontrol circuit means for controlling said amplifier means for varyingthe magnitude of current flowing through said semiconductor means andsaid coil in dependence upon the magnitude of a said induced voltage insaid coil.

1. A system for driving a resonant spring mass system comprising adriver having a driving coil mounted for reciprocation in an air gap ofa magnetic field structure, and means for coupling said driving coil tosaid spring mass system; an amplifier having an input and an output; andmeans coupling said driving coil to both said input and said output ofsaid amplifier to form a selfexcited oscillatory loop circuit fordriving said driver at the mechanical resonant frequency of the combineddriver-spring mass combination, said output of the amplifier issingle-ended for supplying current in only one direction to said drivingcoil during alternate half cycles of the reciprocation thereof, andfurther means are coupled between said driving coil and said amplifierfor responding to the voltage produced across said driving coil duringthe opposite half cycles of the reciprocation thereof for regulating thegain of said amplifier in a direction tending to maintain said voltageconstant.
 2. A system according to claim 1, wherein said loop circuitincludes means for preventing abrupt voltage changes in the oscillatoryvoltage present in said output of the amplifier.
 3. A system accordingto claim 2, wherein said means for preventing abrupt voltage changescomprises a first wave shaping circuit in said amplifier and a secondwave shaping circuit in the coupling between said driving coil and saidinput of the amplifier, one of said wave shaping circuits producing aphase lag on voltages passing therethrough and the other of said waveshaping circuits producing a corresponding phase lead on voltagespassing therethrough such that the net phase change caused by said firstand second wave shaping circuits is substantially zero.
 4. A systemaccording to claim 1, wherein said further means comprises an auxiliaryamplifier circuit, and means for adjusting the gain of said auxiliaryamplifier.
 5. A system according to claim 4, wherein said further meanscomprises a unidirectional conducting device connected in series with acharge storage element across said output of said amplifier, the polingof said unidirectional conducting device being such as to besubstantially non-conducting for current in said one direction.
 6. Asystem according to claim 1, wherein control means are provided forstarting and stopping oscillation of said oscillatory loop circuit, saidcontrol means comprising means for abruptly suppressing the passage ofA.C. signals around said loop when it is desired to stop oscillation,and means operative upon initiation of a stop command for temporarilycausing operation of said further means in a direction tending tomaintain the gain of said amplifier at a maximum level whereby saiddriving coil is dynamically braked.
 7. A system according to claim 5,wherein said driver further includes a stationary compensating coildisposed in said air gap concentrically related to said driving coil andconnected in series opposition to said driving coil.
 8. A systemaccording to claim 7, wherein said compensating coil has substantiallythe same number of turns of substantially the same size conductor atsubstantially the same pitch as said driving coil such that theinductance of said compensating coil is approximately the same as theinductance of said driving coil.
 9. A system for driving a resonantspring mass system comprising a driver having a driving coil mounted forreciprocation in an air gap of a magnetic field structure, and means forcoupling said driving coil to said spring mass system; an amplifierhaving an input and an output; and means coupling said driving coil toboth said input and said output of said amplifier to form a self-excitedoscillatory loop circuit for driving said driver at the mechanicalresonant frequency of the combined driver-spring mass combination,control means for starting and stopping oscillation of said oscillatoryloop circuit, said control means comprising means for abruptlysuppressing the passage of A.C. signals around said loop when it isdesired to stop oscillation, and means operative upon initiation of astop command for temporarily causing operation of said amplifier atmaximum gain whereby said driving coil is dynamically braked.
 10. Asystem for driving a resonant spring mass system comprising a driverhaving a driving coil mounted for reciprocation in an air gap of amagnetic field structure, and means for coupling said driving coil tosaid spring mass system; an amplifier having an input and an output; andmeans coupling said driving coil to both said input and said output ofsaid amplifier to form a self-excited oscillatory loop circuit fordriving said driver at the mechanical resonant frequency of the combineddriver-spring mass combination, control means for starting and stoppingoscillation of said oscillatory loop circuit, said control meanscomprising means for causing said amplifier to operate momentarily atminimum gain upon initiation of a start command to prevent a highvelocity transient in the initial motion of said driving coil.
 11. Acontrol device for energizing an electro-mechanical driver for driving aresonant spring mass system, said device comprising in combination ahigh gain voltage amplifier having an input and an output, a poweramplifier having an input and a single-ended output, a low pass typefilter netwoRk interconnecting said output of said voltage amplifierwith said input of said power amplifier, said output of said poweramplifier having a first output terminal connected to a point of fixedpotential and having a second output terminal, a high pass type filternetwork interconnecting said second output terminal with said input ofsaid voltage amplifier for providing regenerative feedback thereto, saidfilters being arranged to impose substantially equal and opposite phaseshift on the signal voltage passing therethrough, and means selectablyoperable for selectively preventing oscillation around the loopincluding said two amplifiers when said output terminals are connectedto an electro-mechanical driver.
 12. A control device according to claim11, wherein said means for preventing oscillation comprises a circuithaving a low impedance for A.C. signals, and means for selectablyconnecting said low impedance circuit in shunt with said input of thepower amplifier.
 13. A control device according to claim 11, furthercomprising a unidirectional conducting device connected in series with acharge storage element between said two output terminals, the poling ofsaid unidirectional conducting device being such as to be substantiallynon-conducting for current supplied by said power amplifier, and anauxiliary amplifier having an input coupled across said charge storageelement and having an output connected to said power amplifier forregulating the gain of the latter as a function of the charge on saidstorage device and in a direction tending to maintain said chargeconstant.
 14. A control device according to claim 13, further comprisingmeans operative along with said means for preventing oscillation, uponinitiation of a stop command, for temporarily causing operation of saidauxiliary amplifier such as to tend to maintain the gain of said poweramplifier at a maximum level whereby an effective low impedance shuntappears temporarily across said output terminals.
 15. A vibratory feedercomprising in combination a feeder tray; spring means mounting said trayfor vibratory feed motion; a driver having a driving coil mounted forreciprocation in an air gap of a magnetic field structure; meanscoupling said driving coil to said tray for imparting said motionthereto; an amplifier having an input and an output; and means couplingsaid driving coil to both said input and said output of said amplifierto form a self-excited oscillatory loop circuit for driving said driverat the mechanical resonant frequency of the driver and tray incombination with any load on the tray; said amplifier including meansfor, when activated, applying unidirectional current to flow in a givendirection through said coil; and said coupling means including controlcircuit means connected to said coil for activating said currentapplying means in response to a voltage of a first polarity beingdeveloped across said coil.
 16. A vibratory feeder according to claim15, wherein said amplifier comprises means for constraining the waveshape of voltage signals passing through the amplifier to that whichcauses minimum audible noise to be generated by movement of saiddriver-tray combination.
 17. A vibratory feeder comprising: a feedertray; spring means mounting said tray for reciprocal vibratory movement;a driver including magnetic field producing means for developing amagnetic field across an air gap and a driving coil coupled to saidfeeder tray and to said spring means for reciprocal vibratory movementtherewith in first and second opposing directions in said air gapagainst respectively opposing forces exerted thereon by at least saidspring means so that as said coil moves through said magnetic field avoltage of a first polarity is induced in said coil as it travelsthrough said field in said first direction and a voltage of an oppositesecond polarity is induced in said coil as it travels through said fieldin said second direction; activatable circuit meanS for, when activated,applying unidirectional current to said coil to flow therethrough in agiven direction to develop driving forces imparting movement to saidcoil in said first direction; first control circuit means connected tosaid coil and respectively responsive to a said induced voltage of saidfirst polarity for activating said current applying circuit means and toa said induced voltage of said second polarity for de-activating saidcurrent applying means whereby unidirectional current is periodicallyapplied in said given direction to said coil at a frequency essentiallycorresponding with the mechanical resonant frequency of the driver coil,spring means and tray and any load carried by the tray.
 18. A vibratoryfeeder as set forth in claim 17 wherein said current applying circuitmeans includes semiconductor means for, when conducting, completing apath for said unidirectional current to flow in said given directionthrough said coil with the amount of current flowing therethroughvarying as a function of the level of conductivity of saidsemiconductive means.
 19. A vibratory feeder as set forth in claim 18wherein said current applying means includes amplifier means for varyingthe magnitude of current flowing through said semi-conductor means andsaid coil, second control circuit means for controlling said amplifiermeans for varying the magnitude of current flowing through saidsemiconductor means and said coil in dependence upon the magnitude of asaid induced voltage in said coil.